Reciprocity

The Rule of Reciprocity

• Using the rule of reciprocity is the key to being a pro photographer.  Your camera meter may indicate an exposure that works for the scene, but if you know the rule of reciprocity, you can choose a wide variety of exposure settings.  

• Reciprocity is when you add a "stop" of light entering the camera with one of the exposure controls (either the f/stop or shutter speed) and balance it by taking away a "stop" of light with the other.

• A "stop" is a photographic term for twice or half the amount of light. It is the basic control used on all professional level cameras (those with f/stop and shutter speed settings).  Both the f/stop and shutter speed controls can change the amount of light reaching the film in stops.

For example...

• You are outdoors in bright light and the camera’s exposure meter (or light meter) indicates an exposure of f/16@1/125 for your 100 ISO film.   You actually have many other choices for taking that picture.  All of them will allow the same amount of light to reach the film and expose the film properly.

What other choices do you have?

1 2 4 8 15 30 60 125 250 500 1000Slower Faster

1.4 2 2.8 4 5.6 8 11 16 22 More light Less

light

• You have a meter reading of 125 at f 8. How can you change the settings, maintaining the amount of light coming into the camera? How many other options do you have?

1 2 4 8 15 30 60 125 250 500 1000Slower Faster

1.4 2 2.8 4 5.6 8 11 16 22 More light Less

light

1 2 4 8 15 30 60 125 250 500 1000Slower Faster

1.4 2 2.8 4 5.6 8 11 16 22 More light Less

light

1 2 4 8 15 30 60 125 250 500 1000Slower Faster

1.4 2 2.8 4 5.6 8 11 16 22 More light Less

light

1 2 4 8 15 30 60 125 250 500 1000Slower Faster

1.4 2 2.8 4 5.6 8 11 16 22 More light Less

light

Depth of Field and Reciprocity

• You have a meter reading of 250 at f 4. How can you change the settings, maintaining the amount of light coming into the camera AND shorten your depth of field (ie. Blur the background)?

Reciprocity and Camera Shake

• You have a meter reading of 30 at f 8. • Unless you have a steady hand, you

know that you will have a blurry image due to camera shake at any shutter speed slower than 125.

• How can you change the settings, maintaining the amount of light coming into the camera AND eliminate risk of a blurry image due to camera shake?

Try it out for yourself!• Go to:

http://www.photonhead.com/simcam/

Play with different settings (still using your chart to maintain reciprocity) in the

Shutter/Aperture section to see how it affects the picture

Then take a look at Camera Shake and Film Speed